U.S. patent number 10,006,542 [Application Number 15/329,726] was granted by the patent office on 2018-06-26 for controller for continuously variable transmission.
This patent grant is currently assigned to JATCO Ltd, NISSAN MOTOR CO., LTD.. The grantee listed for this patent is JATCO Ltd, NISSAN MOTOR CO., LTD.. Invention is credited to Kosuke Abe, Tomoyuki Suwabe, Shin Tsukamoto.
United States Patent |
10,006,542 |
Abe , et al. |
June 26, 2018 |
Controller for continuously variable transmission
Abstract
A control device for a continuously variable transmission
includes a wheel speed difference sensing section configured to
sense a wheel speed difference between the driving wheel and the
driven wheel from a detection value of the first rotation speed
sensor and a detection value of the second rotation speed sensor;
and a clamping force increasing section configured to increase a
clamping force for sandwiching a belt of the continuously variable
transmission by a pulley when the wheel speed difference becomes
equal to or greater than a first predetermined value, relative to a
case where the wheel speed difference is smaller than the first
predetermined value.
Inventors: |
Abe; Kosuke (Isehara,
JP), Suwabe; Tomoyuki (Atsugi, JP),
Tsukamoto; Shin (Isehara, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
JATCO Ltd
NISSAN MOTOR CO., LTD. |
Fuji-shi, Shizuoka
Yokohama-shi, Kanagawa |
N/A
N/A |
JP
JP |
|
|
Assignee: |
JATCO Ltd (Fuji-Shi,
JP)
NISSAN MOTOR CO., LTD. (Yokohama-Shi, JP)
|
Family
ID: |
55217231 |
Appl.
No.: |
15/329,726 |
Filed: |
June 24, 2015 |
PCT
Filed: |
June 24, 2015 |
PCT No.: |
PCT/JP2015/068122 |
371(c)(1),(2),(4) Date: |
January 27, 2017 |
PCT
Pub. No.: |
WO2016/017326 |
PCT
Pub. Date: |
February 04, 2016 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
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US 20170219096 A1 |
Aug 3, 2017 |
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Foreign Application Priority Data
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|
|
|
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Jul 30, 2014 [JP] |
|
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2014-154368 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16H
61/66272 (20130101); F16H 59/48 (20130101); F16H
59/46 (20130101); F16H 59/42 (20130101); F16H
61/12 (20130101); F16H 59/40 (20130101); F16H
2059/405 (20130101); F16H 2061/66277 (20130101); F16H
2061/1284 (20130101) |
Current International
Class: |
F16H
59/46 (20060101); F16H 61/662 (20060101); F16H
59/42 (20060101); F16H 59/48 (20060101); F16H
61/12 (20100101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2003-269591 |
|
Sep 2003 |
|
JP |
|
2005-114088 |
|
Apr 2005 |
|
JP |
|
2006-220259 |
|
Aug 2006 |
|
JP |
|
2007-162796 |
|
Jun 2007 |
|
JP |
|
Primary Examiner: Wright; Dirk
Attorney, Agent or Firm: Foley & Lardner LLP
Claims
The invention claimed is:
1. A control device for a continuously variable transmission, the
control device comprising: a first rotation speed sensor arranged
to sense a rotation speed of a driving wheel; a second rotation
speed sensor arranged to sense a rotation speed of a driven wheel;
a wheel speed difference sensing section configured to sense a
wheel speed difference between the driving wheel and the driven
wheel from a detection value of the first rotation speed sensor and
a detection value of the second rotation speed sensor; and a
clamping force increasing section configured to increase a clamping
force for sandwiching a belt of the continuously variable
transmission by a pulley when the wheel speed difference becomes
equal to or greater than a first predetermined value, relative to a
case where the wheel speed difference is smaller than the first
predetermined value, wherein the control device comprises a
vibration sensing section configured to sense a vibration of a
speed of a vehicle based on the detection value of at least one of
the first rotation speed sensor and the second rotation speed
sensor, and an increase releasing section configured to decrease
the clamping force increased by the clamping force increasing
section when the sensed wheel speed difference is equal to or
smaller than a second threshold value, and when the sensed
vibration is equal to or smaller than a third threshold value.
2. The control device for the continuously variable transmission as
claimed in claim 1, wherein the control device comprises a rough
road judging section configured to judge that a traveling road
surface is a rough road when the wheel speed difference becomes
equal to or greater than the first predetermined value.
3. The control device for the continuously variable transmission as
claimed in claim 1, wherein the control device comprises a third
rotation speed sensor arranged to sense a rotation speed of a
primary pulley connected to a side of a driving source, and an
abnormality sensing section configured to sense an abnormal state
of at least one of the first rotation speed sensor and the second
rotation speed sensor; the vibration sensing section is configured
to sense a vibration of the primary pulley from a detection value
of the third rotation speed sensor; and the increase releasing
section is configured not to use the sensed wheel speed difference
when the abnormal state of one of the first rotation speed sensor
and the second rotation speed sensor is sensed, and to decrease the
clamping force increased by the clamping force increasing section
when the vibration sensed from the third rotation speed sensor is
equal to or smaller than a fourth threshold value.
4. A control device for a continuously variable transmission, the
control device comprises: a first rotation speed sensor arranged to
sense a rotation speed of a front driving wheel; a second rotation
speed sensor arranged to sense a rotation speed of a rear driving
wheel; an acceleration sensing section configured to sense an
accelerator of the driving wheel from the detection value of one of
the first rotation speed sensor and the second rotation speed
sensor; a wheel speed difference sensing section configured to
sense a wheel speed difference between the front driving wheel and
the rear driving wheel from the detection values of the first
rotation speed sensor and the second rotation speed sensor; and a
clamping force increasing section configured to increase a clamping
force for sandwiching a belt of the continuously variable
transmission by a pulley when the wheel speed difference becomes
equal to or greater than a first predetermined value, when the
acceleration of the driving wheel is equal to or greater than a
fifth predetermined value, or when the acceleration of the driving
wheel is equal to or smaller than a sixth predetermined value
smaller than the fifth predetermined value, relative to a case in
which the above-conditions are not satisfied, wherein the control
device comprises a vibration sensing section configured to sense a
vibration of a speed of a vehicle based on the detection value of
at least one of the first rotation speed sensor and the second
rotation speed sensor, and an increase releasing section configured
to decrease the clamping force increased by the clamping force
increasing section when the sensed wheel speed difference is equal
to or smaller than a second threshold value, and when the sensed
vibration is equal to or smaller than a third threshold value.
5. The control device for the continuously variable transmission as
claimed in claim 4, wherein the control device comprises a third
rotation speed sensor arranged to sense a rotation speed of a
primary pulley connected to a side of a driving source, and an
abnormality sensing section configured to sense an abnormal state
of at least one of the first rotation speed sensor and the second
rotation speed sensor; the vibration sensing section is configured
to sense a vibration of the primary pulley from a detection value
of the third rotation speed sensor; and the increase releasing
section is configured not to use the sensed wheel speed difference
when the abnormal state of one of the first rotation speed sensor
and the second rotation speed sensor is sensed, and to decrease the
clamping force increased by the clamping force increasing section
when the vibration sensed from the third rotation speed sensor is
equal to or smaller than a fourth threshold value.
Description
TECHNICAL FIELD
This invention relates to a control device for a continuously
variable transmission.
BACKGROUND ART
A patent document 1 discloses an art to accurately judge a state of
a road surface, and to perform a hydraulic control of a clamping
force of a belt type continuously variable transmission which is
appropriate for the actual state of the road surface. In
particular, a band-pass filter processing is performed to a
detection value of a rotation speed of a driving wheel. A value
obtained by that processing is totally-integrated with time. A road
surface state is judged based on that time total integrated value.
When it is judged that the road surface state is a rough road, a
clamping force is increased to be greater than that when a smooth
road is judged.
However, for accurately judging the state of the road surface, the
band-pass filter processing is performed to the detection value,
and the total integration is performed with time. Accordingly, it
takes time to judge. The control to increase the clamping force
does not make it in time even when the rough road is judged.
Consequently, a belt slippage may be generated. For example, on a
road surface whose a road surface frictional coefficient
(hereinafter, described as .mu.) is spotted (dappled), the driving
wheels are slipped on a low .mu. portion, and immediately then
gripped on a high .mu. portion, so that a torque inputted to the
continuously variable transmission is increased. When it takes the
time to judge the rough road on this road surface, the control to
increase the clamping force does not make it in time due to the
response delay of the hydraulic pressure. The slippage is generated
between the belt and the pulleys.
PRIOR ART DOCUMENT
Patent Document
Patent Document 1: Japanese Patent Application Publication No.
2003-269591
SUMMARY OF THE INVENTION
It is an object to provide a control device for a continuously
variable transmission arranged to suppress a belt slippage without
depending on a road surface state.
A control device for a continuously variable transmission according
to the present invention, the control device comprises: a first
rotation speed sensor arranged to sense a rotation speed of a
driving wheel; a second rotation speed sensor arranged to sense a
rotation speed of a driven wheel; a wheel speed difference sensing
section configured to sense a wheel speed difference between the
driving wheel and the driven wheel from a detection value of the
first rotation speed sensor and a detection value of the second
rotation sensor; and a clamping force increasing section configured
to increase a clamping force for sandwiching a belt of the
continuously variable transmission by a pulley when the wheel speed
difference becomes equal to or greater than a first predetermined
value, relative to a case where the wheel speed difference is
smaller than the first predetermined value.
By the present invention, the rough road is judged based on the
wheel speed difference of the rotation speeds of the driving wheel
and the driven wheel. Accordingly, it is possible to immediately
increase the clamping force when the driving wheel is slipped.
Consequently, it is possible to prevent the belt slippage according
to the grip force increase of the driving wheels after the
slippage.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a system diagram showing a configuration of a control
device for a continuously variable transmission according to an
embodiment.
FIG. 2 is a flowchart showing a rough road control operation
according to the embodiment.
FIG. 3 is a control block diagram showing a vehicle speed vibration
component extracting operation in the embodiment.
FIG. 4 is a time chart showing the rough road control operation in
the embodiment.
DESCRIPTION OF EMBODIMENTS
Hereinafter, an embodiment according to the present invention is
illustrated based on the drawings. In this specification, a "smooth
road" is a paved road paved by asphalt, concrete and so on. A
"rough road" is an unpaved road in general, such as a gravel road,
a macadam road and so on. The rough road includes a rough road on
which an obstacle such as a large stone, a wood, and a curbstone,
and/or a road depression portion exist in a travel direction, whose
a road surface is largely recessed and raised, and from which a
sudden torque is inputted from driving wheels to a transmission.
The "sudden torque" is a sudden large torque temporarily inputted
from the driving wheels to the transmission when the vehicle runs
on to the obstacle, or when the idling (racing) wheels are landed
on the road surface again after the vehicle is got over the
obstacle.
FIG. 1 is a system diagram showing a configuration of a control
device of a continuously variable transmission according to the
embodiment. A belt type continuously variable transmission
(hereinafter, referred to as a "CVT") 1 includes a primary pulley 2
and a secondary pulley 3 which are torque transmitting members, and
which are disposed so that V-grooves of the primary pulley 2 and
the secondary pulley 3 are aligned with each other; and a belt 4
wound around the V-grooves of these pulleys 2 and 3. An engine 5 is
disposed coaxially with the primary pulley 2. A torque converter 6
including a lock-up clutch 6c, and a forward/rearward movement
switching mechanism 7 are provided in this order from the engine
5's side between the engine 5 and the primary pulley 2.
The forward/reward movement switching mechanism 7 includes a double
pinion planetary gear set 7a as a main component. The double pinion
planetary gear set 7a includes a sun gear connected through the
torque converter 6 to the engine 5; and a carrier connected to the
primary pulley 2. Moreover, the forward/rearward movement switching
mechanism 7 includes a forward clutch 7b arranged to directly
connect the sun gear and the carrier of the double pinion planetary
gear set 7a; and a rearward brake 7c arranged to fix a ring gear.
At an engagement of the forward clutch 7, an input rotation from
the engine 5 through the torque converter 6 is transmitted directly
to the primary pulley 2. At the engagement of the rearward brake
7c, the input rotation from the engine 5 through the torque
converter 6 is reversed, and then transmitted to the primary pulley
2.
A rotation of the primary pulley 2 is transmitted through the belt
4 to the secondary pulley 3. A rotation of the secondary pulley 3
is transmitted through an output shaft 8, a gear set 9, and a
differential gear device 10 to driving wheels (not shown). For
varying a transmission gear ratio between the primary pulley 2 and
the secondary pulley 3 during transmitting the power, the primary
pulley 2 and the secondary pulley 3 include, respectively, fixed
conical plates 2a and 3a which are conical plates forming the
V-grooves of the primary pulley 2 and the secondary pulley 3; and
movable plates 2b and 3b which are conical plates forming the
V-grooves, and which are arranged to be moved in an axial
direction.
These movable conical plates 2b and 3b are arranged to be urged
toward the fixed conical plates 2a and 3a by supply of a primary
pulley pressure Ppri and a secondary pulley pressure Psec which are
produced based on the line pressure, to a primary pulley chamber 2c
and a secondary pulley chamber 3c. With this, the belt 4 is
frictionally engaged on the conical plates so as to transmit the
power between the primary pulley 2 and the secondary pulley 3. At
the shift, widths of the V-grooves of the pulleys 2 and 3 are
varied by a pressure difference between the primary pulley pressure
Ppri and the secondary pulley pressure Psec that are produced in
accordance with a target transmission gear ratio. With this,
wounding radii of the belt 4 with respect to the pulleys 2 and 3
are continuously varied to attain the target transmission gear
ratio.
A shift control hydraulic circuit 11 controls the primary pulley
pressure Ppri, the secondary pulley pressure Psec, and also
engagement hydraulic pressures of the forward clutch 7b engaged at
the selection of the forward traveling range, and the rearward
clutch 7c engaged at the selection of the rearward traveling range.
The shift control hydraulic circuit 11 performs the control in
response to a signal from a transmission controller 12.
The transmission controller 12 receives a signal from a primary
pulley rotation sensor 13 (corresponding to a third rotation speed
sensor) arranged to sense the rotation speed Npri of the primary
pulley 2, a signal from a secondary pulley rotation sensor 14
arranged to sense the rotation speed Nsec of the secondary pulley
3, a signal from a secondary pulley pressure sensor 14 arranged to
sense a secondary pulley pressure Psec, a signal from an
accelerator operation amount sensor 16 arranged to sense an
operation amount of an accelerator pedal, a selection range signal
from an inhibitor switch 17 arranged to sense a selection lever
position, a signal from an oil temperature sensor 18 arranged to
sense a hydraulic fluid temperature TMP of the CVT 1, signals (the
engine speed, a fuel injection time period and so on) relating to
an input torque Tp from an engine controller 19 configured to
control the engine 5, and a signal from wheel speed sensors 21 (a
wheel speed sensor of front wheels which are driving wheels is
represented as 21R, and a wheel speed sensor of rear wheels which
are driven wheels is represented as 21R) arranged to sense wheel
speeds of the wheels.
The transmission controller 12 calculates a wheel speed difference
of the front and rear wheels from the signal of the wheel speed
sensor 21F of the front wheels which are the driving wheels, and
the signal of the wheel speed sensor 21R of the rear wheels which
are the driven wheels. The transmission controller 12 is configured
to judge the rough road traveling from a magnitude of the wheel
speed difference. Then, when the rough road traveling is judged,
the transmission controller 12 performs a rough road detection
control operation. The rough road detection control operation is to
release (disengage) the lock-up clutch 6c, to output, to the
transmission control hydraulic circuit 11, a command to increase
the secondary pulley pressure Psec (hereinafter, described also as
the clamping force) to a rough road control pressure P1 to increase
torque capacities of the pulleys 2 and 3, and to output, to the
engine controller 19, a command (the fuel injection decrease
command, an intake air amount decrease command and so on) to
decrease the output torque of the engine 5 so as to decrease the
input torque to the CVT 1 to be smaller than the torque capacity of
the pulley. In this way, the rough road judgment is performed based
on the wheel speed sensor signals. Accordingly, it is possible to
rapidly increase the clamping force when the driving wheels are
slipped, and to prevent the belt slippage according to the increase
of the grip forces of the driving wheels after the slippage. With
this, it is possible to provide, to the secondary pulley 3, the
clamping force by which the belt 4 is not slipped even when the
sudden torque is inputted, and thereby to increase the torque
capacity of the secondary pulley 3. Moreover, it is possible to
decrease the input torque to the CVT 1, and to effectively protect
the CVT 1 from the suddenly generated torque.
FIG. 2 is a flowchart showing the rough road control operation in
the embodiment.
At step S1, the rough road detection is performed. When the road is
the rough road, the rough road detection flag is brought to the ON
state. Then, the process proceeds to step S2. Otherwise, when the
road is the smooth road, the process is finished. In this case, the
rough road detection is judged based on whether or not the wheel
speed difference which is a difference between the rotation speed
of the driving wheel that is sensed by the wheel speed sensor 21F,
and the rotation speed of the driven wheel that is sensed by the
wheel speed sensor 21R is equal to or greater than an entering
judgment threshold value (corresponding to a first predetermined
value). When the wheel speed difference is equal to or greater than
the entering judgment threshold value, the rough road is judged, so
that the rough road detection flag is brought to the ON state. When
the wheel speed difference is smaller than the entering threshold
value, the smooth road is judged, so that the rough road detection
flag is brought to the OFF state.
At step S2, the rough road detection control is performed. That is,
the lock-up clutch 6c is released (disengaged), and the secondary
pulley pressure Psec is increased to the rough road control
pressure P1.
At step S3, it is judged whether or not the wheel speed difference
is equal to or smaller than a release judgment threshold value
(corresponding to a second predetermined value). When the wheel
speed difference is equal to or smaller than the release judgment
threshold value, the process proceeds to step S5. When the wheel
speed difference is greater than the release judgment threshold
value, the process proceeds to step S4. The release judgment
threshold value is set to a value smaller than the entering
judgment threshold value.
Besides, it is constantly monitored whether or not there is an
abnormal state (for example, an abnormality of the output value,
wire breaking and so on) of the wheel speed sensors 21 by other
routine (not shown). When the wheel speed sensor 21 is in the
abnormal state, it is judged that it is equal to or smaller than
the release judgment threshold value. The process proceeds to step
S5. With this, it is possible to avoid that the rough road
detection control cannot be released in the abnormal state of the
wheel speed sensor 21. The continuation of the rough road detection
control causes the deterioration of the fuel consumption.
At step S4, the release judgment timer is reset. The process
returns to step S2 to continue the rough road detection control. In
this case, the release judgment timer is a timer arranged to be
counted up when the wheel speed difference is equal to or smaller
than the release judgment threshold value. By permitting the
release when a state where the wheel speed difference is equal to
or smaller than the release judgment threshold value is continued
during the predetermined period, the hunting according to the
judgment is suppressed.
At step S18, a vehicle speed vibration component is extracted from
the wheel speed sensor 21R of the driven wheels. It is judged
whether or not the vehicle speed vibration is equal to or smaller
than a predetermined vibration value (corresponding to a third
predetermined value). When the vehicle speed vibration is equal to
or smaller than the predetermined vibration value, the process
proceeds to step S6. Otherwise, the process returns to step S4 to
reset the release judgment timer.
Hereinafter, the extraction of the vehicle speed vibration
component is illustrated. FIG. 3 is a control block diagram for
performing the vehicle speed component extraction operation in the
embodiment. A vehicle speed conversion section 101 is configured to
convert a wheel speed sensor pulse period (cycle) inputted from the
wheel speed sensor 21R to the vehicle speed. It is possible to
convert from the pulse number inputted during the calculation
period (cycle) to the vehicle speed since the calculation period of
the controller is determined. Next, a bypass filter 102 is
configured to extract only a signal on a high frequency side from
the converted vehicle speed signal. The vehicle speed variation
when the vehicle travels on the smooth road is varied only at the
low frequency by influence of the inertia of the vehicle.
Accordingly, it is conceivable that the signal on the high
frequency side is the vibration component. Next, a low pass filter
103 is configured to smooth the vehicle speed signal on the high
frequency side. In the wheel, a frequency region in which the wheel
can be actually vibrated is limited due to the influence of the
inertia of the wheel. Accordingly, the noise is eliminated
(removed) by the low pass filter 103. The vibration which is
actually generated in the wheel is extracted, so that the vibration
component is extracted.
In the rough road control operation according to the embodiment,
the rough road judgment is performed by using the wheel speed
difference for improving the response of the rough road detection.
Accordingly, if the judgment to finish the rough road detection
control only by using wheel speed difference, the rough road
detection control may be finished by a temporal convergence of the
wheel speed difference even when the road is the rough road. In
this case, even when the rough road judgment is immediately
performed again, there is a problem of the response of the
hydraulic pressure control for increasing the clamping force.
Accordingly, the clamping force may not be increased before the
generation of the belt slippage. On the other hand, in the
embodiment, the judgment of the finish of the rough road detection
control is performed in consideration of the vibration component of
the vehicle speed, in addition to the wheel speed difference.
Consequently, it is possible to avoid the unintentional finish of
the rough road detection control.
Besides, in the abnormal state of the wheel speed sensor 21, the
vibration component is extracted based on the sensor pulse period
sensed by the primary pulley rotation sensor 13. In this case, even
when the transmission gear ratio is varied, the frequency of the
variation of the transmission gear ratio is extremely low.
Accordingly, it is possible to exclude the influence by the low
pass filter. Then, it is judged whether or not the vibration of the
primary pulley 2 is equal to or smaller than a predetermined
vibration value (corresponding to a fourth predetermined value).
When the vibration is equal to or smaller than the predetermined
vibration value, the process proceeds to step S6. Otherwise, the
process returns to step S4 to reset the release judgment timer.
That is, when the wheel speed sensor 21 becomes the abnormal state
and the sensed wheel speed difference becomes large irrespective of
the state of the road, the clamping force becomes large by the
rough road detection control. In this case, it is not possible to
return the clamping force to the low clamping force in the normal
state. Accordingly, the fuel consumption may be deteriorated.
Therefore, the wheel speed difference is not used for the release
judgment in the abnormal state of the wheel speed sensor 21. The
only vibration component of the primary pulley rotation sensor 13
is used for the release judgment. Consequently, when the road
surface state becomes the smooth road, it is possible to return the
clamping force to the low clamping force in the normal state, and
to suppress the deterioration of the fuel consumption.
At step S6, the release judgment timer is counted up.
At step S7, it is judged whether the count value of the release
judgment timer is equal to or smaller than, or equal to or greater
than the predetermined timer value. When the count value is equal
to or greater than the predetermined timer value, the process
proceeds to step S8. Otherwise, the process returns to step S2 to
continue the rough road detection control.
At step S8, the rough road detection flag is brought to the OFF
state, and the rough road detection control is released.
FIG. 4 is a time chart showing the rough road control operation in
the embodiment. Besides, the initial traveling state is a state
where the vehicle travels at a substantially constant speed, where
the rough road detection flag is in the OFF state, and where the
release judgment timer is counted up to the predetermined timer
value.
At time t1, when the vehicle enters the rough road so that the
wheel speed difference exceeds the release judgment threshold
value, the release judgment timer is reset.
At time t2, when the wheel speed difference becomes equal to or
greater than the entering threshold value, the rough road detection
flag is brought from the OFF state to the ON state. The rough road
detection control is performed. With this, the wheel speed
difference is directed in the convergence direction. In this way,
the rough road detection is performed based on the wheel speed
difference. Accordingly, it is possible to rapidly sense the rough
road, and to suppress the belt slippage.
At time t3, the wheel speed difference becomes smaller than the
release judgment threshold value, and the vibration component is
equal to smaller than the predetermined vibration value.
Accordingly, the release judgment timer is started to be counted
up.
At time t4, when the wheel speed difference becomes greater than
the release judgment threshold value again, the count-up of the
release judgment timer is reset. Accordingly, the rough road
detection flag is maintained to the ON state to continue the rough
road detection control. In this way, the rough road detection flag
is set by using the release judgment timer. Consequently, it is
possible to suppress the variation of the clamping force according
to the operation and the non-operation of the rough road detection
control.
At time t5, the road is shifted from the rough road to the smooth
road. The vibration component becomes equal to or smaller than the
predetermined vibration value. Moreover, the wheel speed difference
is smaller than the release judgment threshold value. Accordingly,
the release judgment timer is started to be counted up. Then, at
time t6, when the count value of the release judgment timer is
counted up to the predetermined timer value, the rough road
detection flag is set from the ON state to the OFF state. The rough
road detection control is finished. In this way, at the release of
the rough road detection control, it is possible to further stably
attain the release judgment by judging by the decrease of the
vibration component, in addition to the wheel speed difference.
As explained above, it is possible to attain the following effects
and the following operations in the embodiment.
(1) There are provided the wheel speed sensor 21F (a first rotation
speed sensor) arranged to sense the rotation speed of the driving
wheel;
the wheel speed sensor 21R (a second rotation speed sensor)
arranged to sense the rotation speed of the driven wheel;
the step S1 (the wheel speed difference sensing section) configured
to sense the wheel speed difference of the driving wheel and the
driven wheel from the detection value of the wheel speed sensor 21F
and the detection value of the wheel speed sensor 21R;
the step S1 (the rough road judging section) configured to judge
that the road surface in the traveling is the rough road when the
wheel speed difference becomes equal to or greater than the
entering judgment threshold value (the first predetermined
value);
the step S2 (the clamping force increasing section) configured to
increase the clamping force for sandwiching the belt of the
continuously variable transmission by the pulley hydraulically
controlled when the rough road is judged, relative to a case where
the rough road is not judged;
the step S5 configured to sense the vibration of the vehicle speed
based on the detection value of the wheel speed sensor 21R (at
least one of the first rotation speed sensor and the second
rotation speed sensor); and
the step S8 (the increase release section) configured to decrease
the clamping force increased by the step S2 (the clamping force
increase section) when the sensed wheel speed difference is equal
to or smaller than the release judgment threshold value (the second
predetermined value), and when the sensed vibration is equal to or
smaller than the predetermined vibration value (the third
predetermined value).
That is, the rough road is judged based on the wheel speed
difference between the driving wheel and the driven wheel.
Accordingly, it is possible to immediately increase the clamping
force when the driving wheel is slipped. Consequently, it is
possible to prevent the belt slippage according to the increase of
the grip force of the driving wheels after the slippage.
Moreover, the increased clamping force is decreased after the wheel
speed difference and the vibration of the vehicle speed are
decreased, respectively, equal to or smaller than the predetermined
values. Accordingly, it is possible to accurately judge the escape
from of the rough road. Moreover, it is possible to avoid the
decrease of the clamping force irrespective of the state where the
vehicle travels on the rough road on which the input torque is
suddenly increased, and to prevent the belt slippage.
Furthermore, the clamping force is decreased to the clamping force
according to the smooth road when the wheel speed difference and
the vibration of the vehicle speed are converged. Accordingly, it
is possible to decrease the time period during which the vehicle
travels in the state where the clamping forces are unnecessarily
high even when the road is returned to the smooth road.
(2) There are provided the primary pulley rotation sensor 13 (the
third rotation speed sensor) arranged to sense the rotation speed
of the primary pulley 2 connected to the side of the engine 5 (the
driving source); and the sensor abnormality sensing section
arranged to sense the abnormal state of at least one of the wheel
speed sensor 21F and the wheel speed sensor 21R. The step S5 (the
vibration sensing section) is configured to sense the vibration of
the rotation speed of the primary pulley 2 from the detection value
of the primary pulley rotation sensor 13. The step S8 is configured
not to use the sensed wheel speed difference when the abnormality
of the wheel speed sensor 21 is sensed, and to decrease the
clamping force increased by the step S2 when the vibration sensed
from the primary pulley rotation sensor 13 is equal to or smaller
than the predetermined vibration value (the fourth predetermined
value).
Accordingly, in the abnormal state of the wheel speed sensor 21,
the wheel speed difference is not used, and the only vibration
component of the primary pulley rotation sensor 13 is used for the
release judgment. Consequently, it is possible to return the
clamping force to the low clamping force in the normal state when
the road surface state becomes the smooth road, and to suppress the
deterioration of the fuel economy.
Hereinabove, although the present invention is illustrated based on
the one embodiment, the present invention is not limited to the
above described configuration. It is possible to apply the present
invention.
In the above-described embodiment, the present invention is applied
to the front-wheel drive vehicle. However, the present invention is
applicable to the four-wheel drive vehicle. In this case, the
sufficient wheel speed difference may not be generated. Therefore,
in the rough road judgment at step S1, the following two conditions
are introduced as OR condition.
(a) The accelerations of the wheels are calculated. A state in
which the acceleration is greater than an accelerator increase side
entering judgment threshold value (a fifth predetermined value)
that is considered to be increased by the slippage is continued
during a predetermined time period. (b) The accelerations of the
wheels are calculated. A state in which the acceleration is smaller
than an accelerator decrease side entering judgment threshold value
(a sixth predetermined value) that is considered to be decreased by
the obstruct is continued during a predetermined time period.
The acceleration decrease side entering judgment threshold value is
a small value smaller than the acceleration increase side entering
threshold value. In this case, when one of the above-two
conditions, and a condition in which the wheel speed difference
between the front and rear wheels becomes equal to or greater than
the entering threshold value is satisfied, the rough road is
judged. With this, it is possible to effectively sense the rough
road.
Besides, when the rough road detection control is released in a
case where the rough road detection control is released in the
four-wheel drive vehicle after the rough road is judged by the
above-described conditions, the rough road detection control is
released in accordance with the conditions of the wheel speed
difference and the vehicle speed vibration. With this, it is
possible to rapidly decrease the clamping force when the rough road
is misjudged, and thereby to suppress the deterioration of the fuel
economy.
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